The influence of 3x3 bonded retainer on anterior crowding relapse in mandibular incisor extraction cases

ABSTRACT Objective: To evaluate the 3x3 bonded retainer influence on the mandibular anterior crowding in cases treated with mandibular incisor extraction Methods: The sample comprised pretreatment, posttreatment and follow-up orthodontic records of 16 subjects (10 females and 6 males) with Class I malocclusion treated with extraction of a single mandibular incisor. The mean ages (± SD) at pretreatment, posttreatment and follow-up evaluation were 23.45 ± 9.14 years, 25.50 ± 8.95 years and 30.11 ± 8.59 years, respectively. The mean (± SD) treatment time and posttreatment evaluation time were 2.05 ± 0.45 years and 4.60 ± 1.85 years , respectively. Little irregularity index and interdental widths were evaluated using dental casts. The sample was divided into two subgroups, according to the presence of the 3x3 bonded retainer at follow-up. Results: The subgroup without 3x3 bonded retainer presented a greater relapse at the follow-up, when compared to 3x3 bonded retainer subgroup. Conclusion: There was a significant relapse in cases treated with mandibular incisor extraction at follow-up. The subgroup without 3x3 bonded retainer showed a significant relapse at the follow-up when compared to the retainer group.


INTRODUCTION
Retention and stability are always a concern for orthodontists.
Maintaining a stable orthodontic treatment over the years posttreatment is a challenge. Several long-term retention studies evaluating the stability of different treatment modalities have reported that some relapse can be expected irrespective of initial malocclusion or type of treatment. [1][2][3] Most of the researches is centered on the mandibular anterior crowding relapse. [4][5][6] Long-term follow-up studies show that long-term response to mandibular anterior alignment is unpredictable; furthermore, parameters such as initial crowding, age, sex, Angle classification, maxillary and mandibular incisor proclination, horizontal and vertical growth amounts have not been useful in establishing a prognosis. 7,8 It has also been shown that two thirds of the patients presented unsatisfactory mandibular anterior alignment after retention, and crowding continues to increase during the 10 to 20 years posttreatment. 7,9 Mandibular anterior crowding is the most common malocclusion feature found in the population 10 and several treatment modalities can be employed for treatment, such as distal movement of posterior teeth, lateral movement of canines, labial movement of incisors, interproximal enamel reduction, premolars extraction, incisors extractions or even a combination of the above mentioned. In cases treated nonextraction, crowding resolution is performed by an increase in arch perimeter, Berbert M, Cotrin P, Oliveira RCG, Oliveira RG, Valarelli FP, Freitas MR, Freitas KMS -The influence of 3x3 bonded retainer on anterior crowding relapse in mandibular incisor extraction cases 5 achieved by generalized expansion of the buccal segments, along with advancement of the mandibular incisors. 11 Despite these changes may be consistent with certain treatment objectives; in others, they may be undesirable.
Mandibular incisor extraction is indicated in carefully selected cases to resolve crowding, especially when space requirements and facial esthetics do not call for greater dental movements.
Incisor extraction is effective in treating Class I malocclusion in permanent dentition with moderate anterior mandibular crowding. [12][13][14] The intentional extraction of a mandibular incisor can enable the orthodontist to produce enhanced functional occlusal and cosmetic results with minimal orthodontic manipulation. 15 There are four classical indications for mandibular incisor extraction: anomalies in the number of anterior teeth; tooth size anomalies, ectopic eruption of incisors and moderate Class III malocclusions. 16  Berbert M, Cotrin P, Oliveira RCG, Oliveira RG, Valarelli FP, Freitas MR, Freitas KMS -The influence of 3x3 bonded retainer on anterior crowding relapse in mandibular incisor extraction cases 6 It is known that occlusal relapse can be expected after active orthodontic treatment irrespective of long-term use of fixed retainers, 18 while some authors 9,19,20 state that a fixed retainer should be in place to ensure long-term mandibular anterior alignment. Few researches have been conducted to evaluate protocols and trends in orthodontic retention, and the quality of the available evidence is low. Regarding mandibular anterior teeth, there is a lack of published evidence to guide the clinical practice of orthodontic retention and relapse management. [21][22][23][24] The aim of this study was to evaluate if the 3x3 bonded mandibular retainer influences the relapse of anterior crowding in cases treated with mandibular incisor extraction.

This retrospective study was approved by the Ethics in Human
Research Committee at Centro Universitário Ingá under number 61629516.7.0000.5220.
Sample size calculation was performed based on an alpha significance level of 5% and beta of 20% to detect a minimum difference of 0.35mm with a standard deviation of 0.34mm for the Little Irregularity Index. 25  Data were collected according to the following inclusion criteria: Class I malocclusion patients with straight profile, mild to moderate mandibular anterior crowding, maxillary teeth generally well aligned, with the dental midline coincident with the facial midline, complete permanent dentition up to first permanent molars at the beginning of treatment, no dental agenesis, no tooth shape or number abnormalities, and no previous orthodontic treatment performed with mandibular incisor extraction.
Comprehensive orthodontic treatment was carried out with The tooth-size discrepancy created by the incisor extraction, when confirmed through Bolton analysis, was compensated with maxillary incisor enamel reduction. No dental stripping was performed in the mandibular dentition.
At the end of treatment, all patients used a maxillary removable retainer (Hawley plate) and a 3x3 fixed retainer made with thick (0.025-in) round stainless steel wire bonded in all teeth from right to left mandibular canine (3-3) (Fig 1). All patients presented adequate protrusive anterior guidance and disocclusion lateral guidance in group function at the end of treatment. At 1 year posttreatment follow-up, all patients still had the 3x3 bonded mandibular retainer in place. This information was obtained from the patients' records. In the last follow-up recall (T 3 ), some patients still had the 3x3 bonded mandibular retainer in place and some, due to personal reasons, did not.
Thus, the sample was divided into two groups, according to   » 3-3 width: distance between the crown tips of the right and left mandibular canines (Fig 3).

RESULTS
The random errors varied from 0.15 (Little Irregularity Index) to 0.31 (3-3 width). There was no significant systematic error.
Little Irregularity Index was significantly reduced with treatment, and showed a significant relapse at follow-up (Table 1).
Overjet was corrected with treatment and remained stable in the follow-up. Overbite was maintained with treatment and increased significantly in the follow-up. Intercanine width was significantly reduced at T 2 and remained stable at T 3 ( Table 1). The 4-4, 5-5 and 6-6 widths presented similar patterns of change, increasing with treatment and showing a slight decrease at the long-term follow-up (Table 1).
Ages, treatment time and long-term follow-up evaluation were comparable in both groups ( Table 2).
The groups were comparable regarding Little Irregularity Index at pretreatment (Table 3). Both groups showed similar crowding correction at posttreatment (   Overbite was significantly greater in the group without retainer at T 3 ( Table 3). The changes in overbite from posttreatment to long-term follow-up were greater in the group without retainer (Table 3).
There was no statistically significant difference for the man-    These combination of factors favors an efficient and adequate orthodontic treatment plan, and is in accordance with the current literature. [12][13][14] The the studies say about one of the major advantages of incisor extraction, which is the maintenance of interdental distances, mainly the intercanine width. 12 The subgroups were comparable regarding initial, final and follow-up ages, treatment time and follow-up stage ( Table 2).
The initial mean age was over 21 years old, and at the follow-up stage, patients were over 28 years. This finding shows that patients had no residual growth that may have influenced the relapse. 31,32 The majority of long-term studies presents a sample with a lower initial age, and, sometimes the follow-up stage coincides with the end of growth, and crowding often cannot be differentiated from the occlusal maturational changes. 33,34 Berbert M, Cotrin P, Oliveira RCG, Oliveira RG, Valarelli FP, Freitas MR, Freitas KMS -The influence of 3x3 bonded retainer on anterior crowding relapse in mandibular incisor extraction cases 20 In the follow-up stage, the subgroup without retainer presented a significant relapse when compared to the retainer subgroup (Table 3). According to Little, to obtain a significant value of crowding relapse in the postretention stage, the index must be greater than 3.5 mm. In the present study, the group without retention presented a mean (±SD) Little index of 2.27±0.80 at T 3 , and this is not considered a great crowding at the follow-up. However, this parameter was significantly greater than in Group 2. This result is in agreement with other studies 18,20 , in which mandibular anterior alignment was significantly better for the group using a 3x3 fixed retainer. This result was already expected, since the 3x3 bonded retainer aims at keeping the alignment and preventing relapse. However, Lang et al 19 found that some degree of relapse could be observed even in patients with long-term bonded retention. 35,36 According to Little et al, 9 the only way to ensure continued satisfactory alignment posttreatment probably is by the use of fixed retention for lifetime.
The group without retainer presented greater overbite at T 3 than the retainer group, and the changes in overbite from posttreatment to the long-term follow-up stage were greater in the no-retainer group (Table 3). This increase in overbite is expected in mandibular extraction cases. 12 However, the no retainer group presented greater overbite and significant The interdental distances showed no difference at the follow-up stage between the no retainer and retainer subgroups (Table 4). This is in agreement with other studies. 36,38 However, these studies did not evaluate orthodontic treatment performed with mandibular incisor extraction. There is no report in the literature comparing these measures in cases of incisor extraction with or without 3x3 bonded retainer at the follow-up stages.

CLINICAL IMPLICATIONS
Despite the study suggesting that alignment stability seems to be better in incisor extraction cases than that achieved in cases subjected to premolar extraction, 16 it was possible to observe a significant anterior crowding relapse in this study.
Little 26 stated that the evidence of progressive instability of the orthodontic treatment is always first noticed by the mandibular anterior crowding after the removal of the retainers.